Issue #1370 - Part 3: Implement content keyword for flex-basis property

Partially based on https://bugzilla.mozilla.org/show_bug.cgi?id=1105111

layout/generic/nsContainerFrame.cpp

@@ -947,8 +947,29 @@ nsContainerFrame::ComputeAutoSize(nsRenderingContext* aRenderingContext,
                        aBorder.ISize(aWM) - aPadding.ISize(aWM);
   // replaced elements always shrink-wrap
   if ((aFlags & ComputeSizeFlags::eShrinkWrap) || IsFrameOfType(eReplaced)) {
-    // don't bother setting it if the result won't be used
-    if (StylePosition()->ISize(aWM).GetUnit() == eStyleUnit_Auto) {
+    const nsStylePosition* position = StylePosition();
+
+    bool isFlexBasisContent = false;
+    if (IsFlexItem()) {
+      uint32_t flexDirection =
+        GetParent()->StylePosition()->mFlexDirection;
+      bool isInlineFlexItem =
+        flexDirection == NS_STYLE_FLEX_DIRECTION_ROW ||
+        flexDirection == NS_STYLE_FLEX_DIRECTION_ROW_REVERSE;
+      isFlexBasisContent =
+        position->mFlexBasis.GetUnit() == eStyleUnit_Enumerated &&
+        position->mFlexBasis.GetIntValue() == NS_STYLE_FLEX_BASIS_CONTENT &&
+        isInlineFlexItem;
+    }
+
+    // Only bother computing our 'auto' ISize if the result will be used.
+    // It'll be used under two scenarios:
+    // - If our ISize property is itself 'auto'.
+    // - If we're using flex-basis in place of our ISize property (i.e. we're a
+    // flex item with our inline axis being the main axis), AND we have
+    // flex-basis:content.
+    bool isAuto = position->ISize(aWM).GetUnit() == eStyleUnit_Auto;
+    if (isAuto || isFlexBasisContent) {
       result.ISize(aWM) = ShrinkWidthToFit(aRenderingContext, availBased, aFlags);
     }
   } else {

layout/generic/nsFrame.cpp

@@ -4647,11 +4647,23 @@ nsFrame::SetCoordToFlexBasis(bool aIsInlineFlexItem,
     return;
   }
 
+  const nsStyleCoord* newCoord = aFlexBasis;
+
+  // Having 'content' as the value of the 'flex-basis' property is
+  // equivalent to setting both 'flex-basis' and the main size
+  // properties to 'auto', which is why a dummy 'auto' value will
+  // be used here for the main size property.
+  if (aFlexBasis->GetUnit() == eStyleUnit_Enumerated &&
+      aFlexBasis->GetIntValue() == NS_STYLE_FLEX_BASIS_CONTENT) {
+    static const nsStyleCoord autoStyleCoord(eStyleUnit_Auto);
+    newCoord = &autoStyleCoord;
+  }
+
   // Override whichever styleCoord is in the flex container's main axis
   if (aIsInlineFlexItem) {
-    *aInlineStyle = aFlexBasis;
+    *aInlineStyle = newCoord;
   } else {
-    *aBlockStyle = aFlexBasis;
+    *aBlockStyle = newCoord;
   }
 }
 

layout/style/nsCSSKeywordList.h

@@ -205,6 +205,7 @@ CSS_KEY(column, column)
 CSS_KEY(column-reverse, column_reverse)
 CSS_KEY(condensed, condensed)
 CSS_KEY(contain, contain)
+CSS_KEY(content, content)
 CSS_KEY(content-box, content_box)
 CSS_KEY(contents, contents)
 CSS_KEY(context-fill, context_fill)

layout/style/nsCSSParser.cpp

@@ -8592,7 +8592,7 @@ CSSParserImpl::ParseFlex()
   // "a unitless zero that is not already preceded by two flex factors must be
   //  interpreted as a flex factor.
   if (ParseNonNegativeVariant(tmpVal, flexBasisVariantMask | VARIANT_NUMBER,
-                              nsCSSProps::kWidthKTable) != CSSParseResult::Ok) {
+                              nsCSSProps::kFlexBasisKTable) != CSSParseResult::Ok) {
     // First component was not a valid flex-basis or flex-grow value. Fail.
     return false;
   }
@@ -8641,7 +8641,7 @@ CSSParserImpl::ParseFlex()
     if (!wasFirstComponentFlexBasis) {
       CSSParseResult result =
         ParseNonNegativeVariant(tmpVal, flexBasisVariantMask,
-                                nsCSSProps::kWidthKTable);
+                                nsCSSProps::kFlexBasisKTable);
       if (result == CSSParseResult::Error) {
         return false;
       } else if (result == CSSParseResult::Ok) {

layout/style/nsCSSPropList.h

@@ -1758,7 +1758,7 @@ CSS_PROP_POSITION(
     // its own code to parse each subproperty. It does not depend on the
     // longhand parsing defined here.
     VARIANT_AHKLP | VARIANT_CALC,
-    kWidthKTable,
+    kFlexBasisKTable,
     offsetof(nsStylePosition, mFlexBasis),
     eStyleAnimType_Coord)
 CSS_PROP_POSITION(

layout/style/nsCSSProps.cpp

@@ -2263,6 +2263,20 @@ const KTableEntry nsCSSProps::kWidthKTable[] = {
   { eCSSKeyword_UNKNOWN, -1 }
 };
 
+// This must be the same as kWidthKTable, but just with 'content' added:
+const KTableEntry nsCSSProps::kFlexBasisKTable[] = {
+  { eCSSKeyword__moz_max_content, NS_STYLE_WIDTH_MAX_CONTENT },
+  { eCSSKeyword__moz_min_content, NS_STYLE_WIDTH_MIN_CONTENT },
+  { eCSSKeyword__moz_fit_content, NS_STYLE_WIDTH_FIT_CONTENT },
+  { eCSSKeyword__moz_available,   NS_STYLE_WIDTH_AVAILABLE },
+  { eCSSKeyword_content,          NS_STYLE_FLEX_BASIS_CONTENT },
+  { eCSSKeyword_UNKNOWN, -1 }
+};
+static_assert(ArrayLength(nsCSSProps::kFlexBasisKTable) ==
+              ArrayLength(nsCSSProps::kWidthKTable) + 1,
+              "kFlexBasisKTable should have the same entries as "
+              "kWidthKTable, plus one more for 'content'");
+
 const KTableEntry nsCSSProps::kWindowDraggingKTable[] = {
   { eCSSKeyword_default, StyleWindowDragging::Default },
   { eCSSKeyword_drag, StyleWindowDragging::Drag },

layout/style/nsCSSProps.h

@@ -892,6 +892,7 @@ public:
   static const KTableEntry kVolumeKTable[];
   static const KTableEntry kWhitespaceKTable[];
   static const KTableEntry kWidthKTable[]; // also min-width, max-width
+  static const KTableEntry kFlexBasisKTable[];
   static const KTableEntry kWindowDraggingKTable[];
   static const KTableEntry kWindowShadowKTable[];
   static const KTableEntry kWordBreakKTable[];

layout/style/nsComputedDOMStyle.cpp

@@ -4424,7 +4424,7 @@ nsComputedDOMStyle::DoGetFlexBasis()
   //   }
 
   SetValueToCoord(val, StylePosition()->mFlexBasis, true,
-                  nullptr, nsCSSProps::kWidthKTable);
+                  nullptr, nsCSSProps::kFlexBasisKTable);
   return val.forget();
 }
 

layout/style/nsStyleConsts.h

@@ -778,6 +778,12 @@ enum class StyleDisplay : uint8_t {
 #define NS_STYLE_WIDTH_MIN_CONTENT              1
 #define NS_STYLE_WIDTH_FIT_CONTENT              2
 #define NS_STYLE_WIDTH_AVAILABLE                3
+// The 'content' keyword is only valid for 'flex-basis' (not for 'width').
+// Since the 'flex-basis' property accepts exactly the same values as 'width',
+// this 'flex-basis'-specific enumerated value is listed alongside the
+// 'width' ones, to be sure we don't accidentally overload this numeric
+// value with two different meanings if new 'width' keywords are added.
+#define NS_STYLE_FLEX_BASIS_CONTENT             4
 
 // See nsStyleDisplay.mPosition
 #define NS_STYLE_POSITION_STATIC                0